Transparent liquid resin material for SMT-enabled LED-applications at higher temperatures and higher luminosities

ABSTRACT

A casting resin compound as an assembly and encapsulation material for electronic and optoelectronic component parts, modules and components, for example for casting out optoelectronic components on the basis of acid anhydride-curable epoxy compounds, particularly bisphenol A-diglycidyl ether, contains multi-functional epoxy novolak resins, particularly an epoxy cresol novolak. This casting resin compound exhibits a clearly increased glass transition temperature, is suitable for mass-production, exhibits no health deteriorations, and supplies SMT-capable products that can be utilized in the automotive sector.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.10/048,667 which was filed with the U.S. Patent and Trademark Office onJun. 14, 2002 based on PCT/DE00/02614 filed on Aug. 4, 2000. Priority isclaimed for this invention and application, corresponding application(s)having been filed in Germany on Aug. 4, 1999, No. 199 36 605.5.

BACKGROUND OF THE INVENTION Field of the Invention

The invention is directed to a transparent casting resin compound forcasting out optoelectronic components.

Opto-electronic components must be protected against adverseenvironmental influences to be functionally reliable and to havedependable utilization with up to 100,000 operating hours. Due toadvantageous thermal-mechanical as well as electrical characteristic,high-purity epoxy resins are often utilized in electrical engineeringand electronics. Epoxy resins have an extraordinarily high chemicalstability for plastics and are therefore employed for the encapsulationof light-emitting diodes (LEDs) at operating temperatures of currentlyup to 110° C. The transparent and non-yellowing duromer materialsexhibit glass transition temperatures of usually up to 120° C. Withincreasing power density and integration density in the field ofopto-electronics, crack-resistant, highly loadable compounds of epoxyresin shaped materials having glass transition temperatures of above130° C. are demanded. In addition to increased operating temperatures,the quality standards must be qualified under aggravated temperaturecycles and temperature shock conditions for innovative LED applicationsin the automotive sector. The encapsulation materials must be completelycured in any case in order to avoid electrical degradation of thecomponent during operation.

The epoxy casting resin shaped materials disclosed by DE 2642465composed of cycloaliphatic casting resin mixtures with epoxies of theglycidylether type exhibit high glass transition temperatures >130° C.but appear unsuitable for fabrication use because of possiblyexcessively high health risks. Toxilogical investigations, which weremade by leading institutions of these resin mixtures, yielded asubstantiated suspicion of pronounced carcinogenic potential in thiscontext.

DE 32 41 767 A1 discloses a colored casting compound on the basis ofcycloaliphatic and aromatic epoxies and carboxylic acid anhydridehardening agents are known that are distinguished by their good colorstability and that are proposed for optical applications.

SMD-LEDs are currently encapsulated with two-component, thermallycross-linking reaction resins on a basis of anhydride-epoxy castingresin. The optimized rheological and thermally reactive properties ofthe casting compound allow cost-efficient mass production processes. Theepoxy resin component is composed of a moderately viscousbisphenol-A-diglycidylether with reactive epoxy diluent, andanti-foaming mixture as well as a pigment batch that enables transparentshaped materials after the hardening step. This A-component can be lacedfurther with low-molecular alcohols. Pigments that can be distributedwith molecular dispersion are utilized for pigmentation. Diffuselylight-emitting components are utilized by adding specific diffuserpastes on the basis of inorganic pigments. Different zinc-saltaccelerated anhydrides are modified with acidic ester upon addition ofoxidation stabilizers for the hardener component. With existing castingcompound, the increase in quality features of future LED generations,however, cannot be adequately satisfied in view of a temperature rangeof utilization and a thermal fatigue resistance according to automotivestandards.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to specify a castingresin compound that exhibits a greater utilization temperature range,particularly a higher glass transition temperature, and also exhibitslow health risks at the same time.

Further, the products manufactured therewith should be capable of beingemployed in all standard soldering methods and should assure shorthardening cycles in mass-production processes. For light-emitting diodeshaving high luminosities, transparent shaped materials that arecolor-stable both thermally as well as photo-chemically are required.

This object is achieved with a transparent casting resin compound forcasting out optoelectronic components on the basis of an acidanhydride-curable epoxy compound. The resin is produced by mixing froman A-component, a B-component, in the weight ratio of a range from100:100 to 100:80, and, optimally, a further additive. The resin has aviscosity at 25° C. of less than 3000 mPas and has a glass transitiontemperature of the shaped material resulting therefrom of above 130° C.A-component is composed of a mixture of at least one epoxy compoundcomprising a diglycidyl ether of bisphenol-A, with the prescription thatcycloaliphatic epoxy compounds are excluded and at least one epoxynovolak resin as a multi-functional epoxy with a proportion of 20-50weight % in the A-component. The B-component comprises a zinc saltaccelerator and contain a carboxylic acid anhydride, such ashexahydrophthalic acid anhydride. In accordance therewith, the inventiondiscloses a transparent casting resin compound as an encapsulation andassembly material for casting out opto-electronic components on thebasis of an acid anhydride-curable epoxy compound that is produced bymixture of an A-component composed of at least one epoxy compound and atleast one multiple-functional epoxy novolak resin, and, potentially, offurther additives, and a B-component composed of at least one carboxylicacid anhydride.

The inventive transparent epoxy casting resin formulations can beadvantageously processed in an established packaging technology and meetthe optical, electrical and thermal-mechanical quality demands of futureproduct generations in opto-electronics, and particularly exhibit glasstransition temperatures above 130° C. The toxic risk potential of theinitial materials is low based on the state of current knowledge, sothat health risks can be precluded insofar as possible.

Systematic investigations of the fundamental regarding the developmentof low-stress plastic composites in electronics have shown that theglass transition temperatures of epoxy resin molded materials curable byan anhydride on a basis of bisphenol-A-epoxy resin were capable of beingclearly enhanced by the addition of multi-functional epoxy novolakresins. It was also observed that such novolak structures contribute tothe reduction of the shrinkage during the processing and improve themechanical properties. The linearly crack-elastic K_(IC) values andG_(IC) values can likewise be enhanced. What are also the beneficialadhesion values of the high-strength dormer materials in shear tensiontests (DIN 53283) were beneficial preconditions for the use of the epoxynovolak resins in opto-electronics, because it was also found thattemperature-stable and yellowing-resistant reaction resin shapedmaterials could be thus manufactured. Since epoxy novolak resins haveviscosity or, respectively, are solid, the rheological properties ofcorresponding formulations had to be adapted to the requirements incasting resin technology. In addition, it was also necessary to adaptthe reactive behavior in view of the manufacture compatibility andrequired glass transition temperature.

The A-component preferably comprises further additives such as areactive diluent, an alcohol, an adhesion-promoting agent, a flowimprover, an agent for degasification, a diffuser paste, and a componentfor setting the color quotient/pigmentation.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Accordingly, an inventive epoxy casting resin component is preferablycomposed in the following way: Multi-functional epoxy casting resins:<80 weight % (Bisphenol-A-diglycidylether) Epoxy cresol novolak: <50weight % Reactive diluent: (Monoglycidylether) <10 weight % Alcohol: <10weight % Diffuser paste (pigment in epoxy casting resin) <10 weight %Adhesion promoter:  <5 weight % Flow improver: (silicone basis)  <1weight % Degasification agent: (silicone basis)  <1 weight % Componentfor setting the color quotient/pigmentation:  <1 weight % (pigment inepoxy casting resin) Internal parting compound: (silicone basis)  <1weight %.

As in DE 26 42 465, the carboxylic acid anhydride can, for example, be ahexahydrophthalic acid anhydride.

The glass transition temperatures of a shaved material, which iscomposed of the aforementioned exemplary embodiment having a mixingratio A:B of 100:90, amounts to 140° C. 135° C. were obtained for thecomponent under manufacturing conditions. All function-specific andcomponent-specific qualifications according to the most currentstandards of automotive electronics were met.

A specific exemplary embodiment for the A-component is recited below:D.E.R. 332 (Dow Chemical): 78.96 weight % (bisphenol-A-diglycidylether)D.E.N. 438 (Dow Chemical): (epoxy Novolak) 20.00 weight % BYK-A506 (BYKChemie GmbH) a solution of foam  0.20 weight % destroying polysiloxanes:(Degasification agent) Silane A187 (OSi Specialities) γ-  0.80 weight %glycidoxypropyltrimethyoxysilane: (adhesion promoter) Masterbatch 09(CIBA Specialties): (setting the color)  0.05 weight %.

This exemplary embodiment exhibits the following technicalcharacteristics and shaped material properties: Viscosity of the A:Bmixture: 1250 mPas (plate cone, 25° C., D = 500 1/s) Use duration at 30°C. 8 h Glass transition temperature 135 ± 5° C. (DSC, 10 K/min) Shorehardness D 86-88 Water absorption: (stored <0.5 weight % for two weeksin water at 23° C.) Bending modulus (DIN53452) 2750 MPa Flexuralstrength (DIN53452) 150 MPa Flexibility at crack (DIN 53452) 7.2%Transmission at 500 nm: >88% (1 mm shaped material thickness) Colorinterval after 4.6 shaped material aging: (6 weeks at 120° C.) Loss ofmass up to 300° C.: <2%. (TG/DTA, 10 K/min, nitrogen)

Further typical parameters, properties and settings of theaforementioned products and pre-products are:

The viscosity of the epoxy resin component is <15,000 mPas at 25° C.

The viscosity of the A:B reaction resin mixture is 3,000 mPas at 25° C.

The shelf life of the epoxy casting resin component amounts to at leastone year at temperatures up to 30° C.

The use duration of the A:B reaction resin mixture amounts to at leastsix hours at 25° C.

The beneficial reactive behavior of the A:B reaction resin mixtureallows fast curing cycles given dependable component casting inmass-production processes having unit numbers of more then 100 millionper year.

The glass transition temperature of the shaped materials is >130° C.

The water absorption after two weeks being stored in water at 23° C. is<0.5 weight %.

The transmission of a 1 mm thick shaped material in the visible range oflight amounts to >88%.

The color shift after thermal aging at 130° C. after six weeks is <10.

The lenses manufactured with the resin proved radiation-resistant inhigh-intensity LEDs having, for example, 1.4 lm/50 mA. The presentdevelopment of shaped material is distinguished by extraordinaryfracture-mechanical properties with K_(IC) 1.34 MPa/m and G_(IC) 577J/m² and the products encapsulated with the resin can be utilized in allSMT processes and—over and above this—are suited for applications in theautomotive sector (Tg>130° C.!).

The bulk degradation up to 300° C. is <2% (thermal scale, 10 K/min,nitrogen).

Other objects and features of the present invention will become apparentfrom the following detailed description considered in conjunction withthe accompanying drawings. It is to be understood, however, that thedrawings are designed solely for purposes of illustration and not as adefinition of the limits of the invention, for which reference should bemade to the appended claims. It should be further understood that thedrawings are not necessarily drawn to scale and that, unless otherwiseindicated, they are merely intended to conceptually illustrate thestructures and procedures described herein.

1. A transparent casting resin compound, said compound comprising: amixture of an A-component and a B-component in a weight ratio in a rangeof 100:100 through 100:80, said resin compound having a viscosity at 25°C. of less than 3000 mPas and having a glass transition temperature ofthe shaped material resulting therefrom of above 130° C.; saidA-component comprising a mixture of a diglycidyl ether of bisphenol-A,with the prescription that cycloaliphatic epoxy compounds are excluded,and one epoxy novolak resin as a multi-functional epoxy with aproportion of 20-50 weight % in the A-component as the only epoxycomponents of the A-component; and said B-component comprising a zincsalt accelerator and containing at least one carboxylic acid anhydride.2. A transparent casting resin compound according to claim 1, whereinthe epoxy novolak resin is an epoxy cresol novolak.
 3. A transparentcasting resin compound according to claim 1, whereby the A-componentcomprises the following percentage composition: epoxy compound: <80weight % Epoxy novolak resin: 20-50 weight % Reactive diluent: <10weight % Alcohol: <10 weight % Diffuser paste <10 weight % Adhesionpromoter: <5 weight % Flow improver: <1 weight % Degasification agent:<1 weight % Pigment in epoxy casting resin: <1 weight %; and Internalparting compound <11 weight %.


4. A transparent casting resin compound according to claim 3, whereinthe B-component contains 2 through 10 weight % zinc salt accelerator. 5.A transparent casting resin compound according to according to claim 1,wherein the A-component comprises the following percentage composition:bisphenol-A-diglycidylether 78.96 weight %; epoxy novolak 20.00 weight%; Degasification agent 0.20 weight %; adhesion promoter 0.80 weight %;and an agent for setting the color 0.04 weight %


6. A transparent casting resin compound according to claim 1, whereinthe B-component is of a nature so that the specific acceleration allowshardening cycles in the range of minutes for mass-production processes.7. A transparent casting resin compound according to claim 1, whereinthe B-component contains 2 through 10 weight % zinc salt accelerator. 8.A transparent casting resin compound according to claim 1, whereinopto-electronic components include modules.
 9. A transparent castingresin compound according to claim 8, wherein the component includesoptoelectronic couplers, light-emitting diodes, phototransistors,photodiodes and light-emitting diode displays.
 10. A method forutilizing a transparent casting resin compound for encapsulating,covering or enveloping a device comprising: providing the device;preparing the transparent casting resin compound comprising a mixture ofan A-component, a B-component and additives, in a weight ratio in arange of 100:100 to 100:80, said compound having a viscosity of lessthan 3000 mPas at 25° C. and having a glass transition temperature in acured state above 130° C., said A-component comprising a mixture of adiglycidyl ether of bisphenol-A with all cycloaliphatic epoxy compoundsbeing excluded, and one epoxy novolak resin as a multi-functional epoxywith a proportion of 20-50 weight % as the only epoxy component in theA-component, and the B-component comprising a zinc salt accelerator andat least one carboxylic acid anhydride; and coating at least a part ofthe device.
 11. A method according to claim 10, wherein the step ofcoating forms a light guide resin for an opto-electronic coupler.
 12. Amethod according to claim 10, wherein the device to be provided areopto-electronic components.
 13. A method according to claim 10, whereinthe device to be provided is selected from the group consisting oflight-emitting diodes, phototransistors, photodiodes and light-emittingdiode displays.